US2003/0078085 discloses a grain tank cover used in a harvesting device such as a combine harvester. This known grain tank cover comprises four rigid cover panels that are moveably connected around the circumference of the top edge of the grain tank. When the rigid cover panels are in a substantially horizontal position, they together cover the top of the grain tank. Usually, they are in this position when the harvester travels from one harvesting site to the next. An actuator assembly can move the rigid cover panels from the horizontal position into a more upright position, in which the rigid cover panels form an upward extension of the walls of the grain tank.
Between adjacent rigid cover panels, a flexible transition panel is present. When the rigid cover panels are in a horizontal position covering the top of the grain tank, the flexible transition panels are disposed inside the tank, drooping downwardly from the side edges of the rigid cover panels. So, the flexible transition panels do not cover the top of the grain tank when the cover panels are in their horizontal position. When the rigid cover panels are raised, the flexible transition panels rise with the rigid cover panels and extend across the otherwise open spaces between the side edges of the rigid cover panels. By closing these open spaces, the space between the rigid cover panels when they are in the upright position can be used to accommodate an additional amount of harvested crop.
The rigid cover panels have to be strong in order to withstand the mechanical load exerted on them by the harvested crop that is accommodated between them when they are in the upright position. This load can be particularly high when the harvester device is on a sloped surface. This results in the rigid cover panels being heavy and contributes significantly to the total weight of the harvester device, even when as proposed in US2003/0078085 the rigid cover panels are made of plastics. The total weight of a harvester device is of concern, for example, because excessive weight can cause an undesired amount of compacting of the soil and because there are weight limits to vehicles that are allowed on public roads.